Unformatted text preview: liquid at column pressure of 250 psia. Column has a partial condenser,
partial reboiler, and 15 equilibrium stages in the column with feed entering the middle stage.
Distillate rate = 23.0 lbmol/h and reflux rate = 150.0 lbmol/h. SoaveRedlichKwong equation of
state for Kvalues and enthalpies.
Find: Product compositions. Stage temperatures, vapor and liquid flow rates, and
compositions. Reboiler and condenser duties.
Analysis: The calculations were made with the TOWER model (Insideout method) of the
Chemcad program, with the following specifications:
Partial condenser
Top pressure = 250 psia
No condenser or stage pressure drop. Therefore, bottom pressure also = 250 psia
Number of stages = 17 (includes partial condenser and partial reboiler)
Feed stage = 9 from the top
Sidestream from stage 13 from the top, as a vapor at a flow rate of 37 lbmol/h
At the top, reflux rate = 150 lbmol/h
At the bottom, bottoms rate = B = F  D  S = 100  23  37 = 40 lbmol/h
Estimated distillate rate = 23 lbmol/h (actual rate)
Estimated reflux rate = 150 lbmol/h (actual rate)
Estimated temperature of stage 1 = 120oF
Estimated temperature of bottom stage = 300oF
Estimated temperature of stage 2 = 140oF
Although the feed was given as a bubblepoint liquid at 250 psia and 213.9oF, the SRK equation
of state gave a bubblepoint temperature of 210.7oF, which was the value used. Based on the
feed composition below, the distillate rate of 23 lbmol/h corresponded to a desired split between
propane and nbutane. The calculations converged rapidly in 3 outerloop iterations with results
given below and on the following pages. The vapor side stream contains 69.5 mol% nC4.
Condenser duty = 914,000 Btu/h
Reboiler duty = 1,440,000 Btu/h
Top temperature = 124.4oF compared to assumed value of 120oF
Bottom temperature = 290.5oF compared to assumed value of 300oF
Stage 2 temperature = 140.9oF compared to assumed value of 140oF Analysis: (continued) Exercise 10.22 (continued) Analysis: (continued) Exercise 10.22 (continued) Exercise 10.23
Subject: Distillation with an intercooler and an interheater Given: Conditions given in Exercise 10.20 except that an intercooler with a duty of 200,000
Btu/h is placed on the fourth stage from the top (Stage 5 counting the partial condenser), and an
interheater with a duty of 300,000 Btu/h is placed on the fourth stage from the bottom (stage 13
from the top counting the partial condenser). Therefore, the remaining specifications are still a
feed of composition below as a bubblepoint liquid at column pressure of 250 psia. Column has
a partial condenser, partial reboiler, and 15 equilibrium stages in the column with feed entering
the middle stage. Distillate rate = 23.0 lbmol/h and reflux rate = 150.0 lbmol/h. SoaveRedlichKwong equation of state for Kvalues and enthalpies.
Find: Product compositions. Stage temperatures, vapor and liquid flow rates, and
compositions. Reboiler and condenser duties.
Analysis: The calculations were made with the TOWER model (Insideout method) of the
Chemcad program, with the following specifications, where TOWER treats intercooler...
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 Spring '11
 Levicky
 The Land

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